With remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21st century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place.
A lithium secondary battery is very important to realize such a ubiquitous society. The lithium secondary battery may be manufactured by receiving an electrode stack in a receiving part of a battery case together with an electrolyte and thermally bonding the outer edge of the receiving part.
As well-known examples of such an electrode stack, there are a stacked type electrode stack configured to have a structure in which positive electrode plates, separator plates, and negative electrode plates, each having a predetermined size, are repeatedly stacked such that the separator plates are disposed respectively between the positive electrode plates and the negative electrode plates, a wound (jelly-roll) type electrode stack configured to have a structure in which a positive electrode sheet, a separator sheet, and a negative electrode sheet, each having a predetermined size, are stacked such that the separator sheet is disposed between the positive electrode sheet and the negative electrode sheet, and then the separator sheet is wound in one direction, and a stacked and folded type electrode stack configured to have a structure in which a predetermined number of stacked type electrode stacks is arranged on a separator sheet, and then the separator sheet is wound in one direction such that the stacked type electrode stacks are stacked.
FIG. 1 is a typical view showing a curved stacked type electrode stack. For the convenience of description, a structure in which one positive electrode plate 11, one separator plate 12, and one negative electrode plate 13 are stacked is shown in FIG. 1. Alternatively, the electrode stack 10 may include a plurality of positive electrode plates, a plurality of separator plates, and a plurality of negative electrode plates. For the stacked type electrode stack 10 shown in FIG. 1, a large amount of man hours are incurred to stack the positive electrode plate 11, the separator plate 12, and the negative electrode plate 13.
FIG. 2 is a typical view showing a curved jelly-roll type electrode stack. Referring to FIG. 2, when the jelly-roll type electrode stack 20 is bent along an imaginary line X′-X″ perpendicular to a direction in which electrode tabs protrude, stress is concentrated on opposite bent ends A′ and A″ of the jelly-roll type electrode stack 20 with the result that the electrodes of the jelly-roll type electrode stack 20 may be broken.
FIG. 3 is a typical view showing a curved stacked and folded type electrode stack. Referring to FIG. 3, when the stacked and folded type electrode stack 30 is bent along an imaginary line X′-X″ perpendicular to a direction in which electrode tabs protrude, a separator sheet wrinkles at opposite bent ends B′ and B″ of the stacked and folded type electrode stack 30 with the result that the size and external appearance of the stacked and folded type electrode stack 30 may be deteriorated.